1. Field of the Invention
This invention relates to a control system for a rotary shaft which is required to be continuously rotated for turning operations and to be positioned in its direction of rotation, such as the spindle or rotary table of a machine tool.
2. Description of the Prior Art
In a machine tool, turning operations of a workpiece mounted on a spindle is sometimes followed, for example, by milling of the workpiece positioned at a desired commanded angular position. A spindle motor for driving the spindle for the turning operations is very powerful and the rotation during the turning operation is high-speed. Thus, the spindle motor has not been employed to effect positioning of the spindle at a commanded angular position. In the prior art, it is customary to employ both a spindle motor for the turning operations and a motor for the spindle positioning operation. The two motors are selectively driven in accordance with the turning and positioning modes of operation.
Since this conventional system requires two motors and two drive systems the device is bulky and expensive.